Puffing cereal grains



Dec. 23, 1952 c. F. HAUGHEY ET AL 2,622,935

PUFFING CEREAL GRAINS Filed Jan. 26, 1951 INVENTORS Patented Dec. 23, 1952 T. Erickson, Climax, Mich assignors to General Foods Corporation; New 'York, N. Y., a corporation of Delaware Application January-26, 1951, Serial-No. 207,902

13 Claims.

This invention relates to the puffing' of cereal grains and more particularly to the production of pufied cereal products of the well known'and.

widely. used breakfast food type such as pufied wheat, puffed rice, etc.

According to the general practice of the art for many years, such puffed cereal products have been produced in a so-called gun comprising a pressure container in which a batch of the desired grain is heated under steam pressure, after which thecontainer is opened suddenly. to release the pressure, causing the grainsto be. expelled violently therefrom and at the same time to. be puffed dueto the sudden expansion of their contained moisture in the form of vapor or steam. Undertypical operatingconditions, .each batch may be heated or cooked for from fourto eight minutes-to a temperature above 500 F. under a steam pressure of about 175 pounds per square inch. Apart from the fact that. this procedure has the usual disadvantages of a batch operation,- it also produces nonuniform results with respect to the size and other characteristics of the puffed grain. The

grains are very sensitive to the time of their exposure to the high temperature and pressure in the gun, to the amount of drop in pressure which they undergo on openingof the gun, and to the rapidity with'which this-drop in pressure takes place. These conditions can be controlled with I respect to the batch as a whole, but it difficult if not impossible to avoid substantial variations in the treatment of the individual grains of such a batch and especially in the: rapidity of the drop inpressure as'thegrains are being expelled from the gun. Control of these conditions with respect to individual grains becomes more difficult as the sizes of the gun" and thebatch are increased, whereas on the other hand a large number of small batches is obviously undesirable for quantity production.

It has been proposed to minimize the disad vantages of batch operation bythe use of automatic or semi-automatic apparatus in which aplurality of suchgunsare operated in sequencewith overlapping cycles, as for example bycharging one gunwhile another is under steam pressure and while: still another is being-diecharged. However, the apparatusrequiredto effect such operation is complicated andeXpensive, and-in any event the operation of each gun is subject to the above mentioned'defectsof thismethod of, puifing. In an efiort to minimize these defects, it hasalso been-proposed to heat a charge of grain in a pressure container, and

then to open a relatively small discharge outlet so that the pressure in the container forces the mass of grain into the outlet and theindividual grains of the charge: are progressively expelled. V

In this method, however, the time exposure; oi the individual grains tothe high temperature and pressure in the container varies substantially because of the time required to expel the entire charge through the restricted outlet; and as a consequence the puffed grains vary not only in size but alsoin degree ofcooking. Moreoven; forcing the mass of grain into and-through-the; outlet tends to cause clogging of the outlet; with resulting physical distortion and mechanical damage to many of the grains, and with the' further result that some grains are? held up-in-J passing through the:- outlet so that the-pressure drop therein takes placegradually.

One ofthe objects of the present invention'is to provide an improved process forpuffingcereal grains whichis truly continuous in operation and which produces a uniformproduct of high;

quality.

Another object is to provide an improved' process for puffing-cereal grains: in which all" of the individual grains are'subjected to uni form conditions of heating-or cooking-andpressure drop.

Another object is to provide an improved-- process as characterized in the preceding-ob jects wherein the pressure on and in the indi= vidual grains is released with greatrapidity.

A still further-object isto providean improved process of the typecharacterized above inWhi'ch' the individual rains are all'subjected'to' uni-'- form and progressively increasing temperature up to theinstant of pressure-release:

Another object is to provide an improved" process of the above type in' which thecondi tiers of temperature, pressure and timeof ex' posure of the grains'theretocan be controlled readily.

A still further object is to improvethe'quality and uniformity of puffed cereal products; 7

It has been found that the foregoing objects can be accomplished by continuously mo'ving' a:'

stream of loose individual grains through an elon gated confined pressure zone having at its outlet" end an open discharge orifice large enough to per; mit thegrains to pass freely therethrough, andiby. maintaining said zone under steam pressure whijc h causes a high velocity current 'of'steam ,to es'capej continuously through said orifice. The eXp ression loose individual grains is here" used. to mean a freely moving stream of forced. avoided because of the danger of physical distor tion of and mechanical damage to the hotflmoi'st grams, in order to insure continuous;movement' of all grains at the desired'ratewith freeacess" I v grains which are not packed tightly together, in'diiferentiation" from a packed or plugged conveying, system" through which a compacted mass of grain is" Such packing" or plugging should be" of the steam to each grain, and in order to bring the grains to the outlet in loose conditionfor discharge from the pressure zone in the manner hereinafter described. To maintain the desired conditions, the conveyor system should not be filled to capacity; for example, good results are obtained when the per cent of fill is not more than 50% of capacity. Thus speed of travel of the stream of grain through the pressure zone can be regulated to predetermine the time of exposure of each grain to the steam pressure and temperature in said zone, and since the stream of grain moves continuously at the desired speed, all of the individual grains are subjected to uniform heating and cooking conditions and are brought to the same state as they reach the outlet end of said zone.

The grains reaching the vicinity of the orifice, being in loose freely moving condition, are picked up individually by the current of steam and conveyed freely through the orifice, i. e., without clogging the orifice and in most cases without any contact with its walls so that mechanical damage is minimized if not completely avoided. It will be seen that since the speed of movement of the grains through the orifice is very high in comparison with that of the stream of grain passing through the pressure zone, said stream i in effect attenuated as it passes through the orifice and hence the orifice can be much smaller than said stream. In many cases the orifice need be only somewhat larger than the maximum dimensions of the individual grains which are discharged one by one in a continuous stream at high velocity. If the rate of feed of the grain to the pressure zone is increased, however, it may be desirable to increase the size of the orifice surficiently to permit several grains to pass through at one time without clogging. The size of the orifice therefore depends in part on the rate of feed of the grain; it should be proportioned in relation thereto so as to be only large enough to permit free passage of the grain in order to avoid undue consumption or waste of steam. By way of example, good results have been obtained with orifice diameters ranging from to 1", the larger orifice sizes being used With relatively high rates of feed of the grain. Thus each individual grain passes freely through the orifice at the high velocity of the current of steam, and inasmuch as the distance to be traveled in passing through the orifice is small, the pressure on and in each grain is released practically instantaneously and a continuous stream of uniformly cooked and puffed grains is discharged from the orifice.

In practicing the above process, the steam pressure in the pressure zone should be maintained at a value such that the pressure drop through the orifice is sufficient to accomplish the desired puffing. The magnitude of the pressure drop required for this purpose may vary substantially and is not critical. At unduly high pressures (and correspondingly high temperatures) in the pressure zone, some of the grains will be overpuffed and shattered and may have a burned taste, while very low pressures do not produce satisfactory puffing. Within these limitations, however, a fairly Wide range of pressures can be used satisfactorily. Moreover, at any pressure satisfactory for pulling, and with an orifice of restricted area as described above, the velocity of the current of steam passing through the orifice will be ample to release the pressure with great rapidity, the grains traveling from the pressure zone to a region of atmospheric pressure (a distance of say 1") in a small fraction of a second. As a general rule, the pressure may be somewhat less than that heretofore customary in grain pufilng as indicated by the example set forth above; for example, a pressure in the range of 100-160 lbs/sq. in. will give satisfactory results in most cases. Using saturated steam, the corresponding temperature range will be about 340-370 F.

Since the conditions of temperature and pressure are most critical in the immediate vicinity of the discharge orifice, the steam is preferably admitted to the pressure zone at its outlet end, and fills the zone so that the temperature of the grains is progressively increased as they move through the pressure zone to its outlet end. A suitable restricted steam outlet may be provided at or near the inlet end of the pressure zone so that in addition to the high velocity current of steam through the orifice, there is also a more gradual movement of steam back through the pressure zone countercurrent to the stream of grain passing therethrough.

Wetting of the surfaces of the grains by condensed moisture during their passage through either the pressure zone or the nozzle should also be somewhat superheated. As the quality of the steam changes from wet saturated to dry saturated or superheated, there is a, marked increase in the size of the pulls when other conditions remain constant. Excessive superheat, however, may cause the surfaces of the pulled grains to be rough and pitted and is preferably to be avoided in most cases. In the range of pressures and temperatures mentioned above, the degree of superheat preferably should not exceed 40-60, best results being obtained in the range of 0-40" superheat. Also condensation of steam in the pressure zone can be minimized by warming or heating the walls of the zone and by preheating the grain itself before it enters the zone.

Preheating of the grain is desirable for the additional reason that it greatly increases the capacity of the apparatus without sudden or unduly prolonged exposure of the grain to high pressure and temperature. To avoid condensation, the temperature of the grain entering the pressure zone should not be less than about F. and preferably it should be substantially higher to obtain the maximum benefit of preheating. However, excessive preheat will cause discoloration and a. burned taste, and may result in shattered product. As a rule, 260 F. is regarded as a maximum preheat temperature for these reasons.

The accompanying drawing illustrates somewhat diagrammatically a suitable apparatus for carrying out the process described generally above, but it is to be understood that said drawing is by way of example only and is not to be taken as a definition of the limits of the invention, reference being had to the appended claims for this purpose.

In the form shown, the confined pressure zone is established and maintained in a plurality of cylindrical containers I, here shown as five in number, which are disposed in parallel side by side relation and interconnected at alternate ends of the successive pairs as shown at 2. The grain to be pufied enters the inlet end of this apparatus through a feed conduit 3 and the stream of grain passes continuously through the series of containers to the outlet conduit 4 and orifice 5 atthe end of the last container. Anysuitable means can be used for moving the stream of grain through these containers, as by means of gravity feed or any suitable type of conveyor mechanism. For example, conventional screw conveyors can be employed as shown in the case of the first and last containers. Each of these conveyors comprises flights 6 mounted on an arbor l, the arbor shaft 8 passing outwardly through the heads 8 at theends of the containerand through suitable pressure glands It which seal the containers against escape of steam therefrom. The ends of the shafts B can be mounted in any suitable bearings, H, and the several shafts can be. driven in any suitable manner, preferably by any desired type of variable speed driving mechanism so that the time of passage of the grain through the pressurezone and accordingly the time of exposure of the grain to thehigh temperatures and pressures maintained therein can be regulated. A series of containers l is preferred to a single container of equivalent length in order to facilitate the mounting of the arbor shafts and to avoid the necessity. for intermediate bearings which might interfere with the free flow of the grain.

The pressure steam is supplied to the pressure zone at a point adjacent the outlet 4 in any suitable manner. As shown, a steam pipe i2 provided with a pressure control valve I3 is connected to the last container I near its outlet end, the steam thus admitted to the last container filling the entire series of containers with a steam atmosphere and also causing a high velocity current of steam to escape continuously through the outlet Land orifice 5. The size of the orifice determines the steam consumption of the equipment at any given pressure to be maintained. The inlet end of the first container I is also provided with a suitable steam exhaust, and as shown, an exhaust pipe M provided with a bleed valve i5 is connected to the grain inlet conduit 3.

Any suitable means can be employed for admitting the grain to the first container I in such a way as to prevent escape of steam from the container and loss of pressure in the pressure zone. Various known types of pressure locking feed valves can be used for this purpose. For purposes of illustration, the drawing shows a feed hopper I6 delivering grain through a suitable stop valve ll to a feed chamber 53 from which the grain is delivered through a second stop valve I9 to the inlet conduit 3. For a purpose described hereinafter, the feed chamber I8 is provided with a steam inlet pipe and a control valve 21 therein and with a steam exhaust pipe 22 having a control valve 23 therein.

In order to prevent condensation of steam on the wallsof the several containers, they may be externally heated in any suitable manner as by means of steam jackets 2d. As shown, the temperature of each jacket 2 can be individually controlled by means of a steam inlet pipe 25 having a suitable pressure control valve 26 therein, the steam exhausting from the jacket through an exhaust pipe 21, but if desired the jackets may be serially connected and controlled by a single pressure control valve.

In preparing the above equipment for use, steam is admitted to the jackets 24 to warm all of the container walls throughout the pressure zone. With the feed chamber I8 empty, the stop valve I9 is opened and the stop valve I? closed, and the valve 2| is closed and the valve 23 opened. Steam isadmitted to the containers through ,the control valve I 3,..thesteam escaping.

6.. through the nozzle 5 and also passing-back through the series of containers and escaping through the feeder exhaust valve 23. This warming operation is continued until there is no further condensation of moisture on the walls of the containers as indicated by the appearance of the exhaust steam discharged therefrom.

When the apparatusis ready for use, thefeeder exhaust valve 23 isclosed, the stop valve I9 is closed, and the stop valve I1 is opened to admit a measured amount of grain from thehopper: I6

into the feed chamber I8. The-stop valve. I1; is

then closed and the feeder inlet valve 2I is opened to build up a steam pressure in the feed chamber greater than the pressure on the nozzle. 5. At

this point the valve 2| is closed and the valvev I9 is opened so that the charge .of-grain is discharged from the feed chamber through the feed conduit 3 into the end of the first container I where the grain is picked up by-the conveyor 6; Successive charges of grain are thus introduced into the first container at a rate such as to sup ply acontinuous stream of grain of the desired size to the nozzle 5.

As explained above, the size of the orifice opening at the nozzle 5 should be large enough to permit the stream of grain to pass freely therethrcugh at high velocity without clogging the orifice opening and without physical distortion or mechanical damage to the grains. As the rate of feed of the grain is increased, therefore, the size of the orifice opening must also beincreased and the steam consumption is increased correspondingly. The proper proportioning of these factors depends on the desired capacity of the apparatus. Within reasonable limits, the rate of feed of the grain can be varied by regulating the speed of rotation of the screw conveyor to permit variations in production without change of the nozzle 5.

The nozzle and orifice may have any suitable shape, good results having been obtained with nozzles of Venturi shape, with simple orifice plates, and with a nozzle of the form shown in the drawing having a tapering passage leading to a relatively small orifice opening. Any other desired type of nozzle or orifice can be employed.

In operation, the bleed valve l5 permits a continuous gradual flow of steam from the inlet pipe IZ through the seri s of containers to the grain feed pipe 3, the steam thus moving ccuntercurrently to the stream of grain fed by the conveyors t. Accordingly the temperature of the grain is progressively increased as it moves through the pressure zone to its outlet end, and as long as the rate of feed is maintained constant, each individual grain is subjected to uniform heating and cooking conditions during its passage through the pressure zone. reheating of the grain as described above enables the length of the pressure zone to be decreased and the capacity of the equipment to be greatly increased.

Furthermore, the preheating cf the grainravoids.

form feed of the grain through the pressure zone,

and maintain the individual grains in loose condition so that they can be picked up readily and carried through the nozzle 5' by the steam current.

The following is an example of processes em bodying the invention as practiced in apparatus of the type described above and illustrated in the drawings:

Amber durum wheat having a bulk density of about 46 lbs. per cubic foot and a moisture content of about 9.5%, the bran coat being largely removed, was preheated to a temperature of 230 F. and introduced into the pressure zone through the hopper I6 and feed chamber l8 as described above. The walls of the zone were heated by maintaining a steam pressure of 240 lbs/sq. in. (gauge) in the jackets 24. The rate of feed of the grain was 1800 lbs. per hour, and the speed of the conveyors was adjusted to provide 'a holdup time in the pressure zone of 2 minutes.

Dry saturated steam at a pressure of 240 lbs./ sq. in. was supplied to the pipe 12 and the reducing valve l3 was set to maintain a pressure in the pressure zone and on the nozzle orifice of approximately 140 lbs/sq. in. (gauge), the temperature being 375 F. The diameter of the orifice opening was /5. Under these conditions a continuous stream of individual pufied grains issued at high velocity from the orifice, the grains being uniformly cooked and puffed and constituting a puffed-wheat product of uniformly high quality having a moisture content of 7% and a bulk density of only 4 lbs. per cubic foot.

It will be understood that the invention is not restricted to the details of the foregoing description and example, and that various changes may be made in the practical operation of the process without departing from the spirit of the invention. Also the apparatus illustrated in the drawing is by way of example only, and the process can be carried out in various other forms of apparatus capable of producing equivalent results, as will be apparent to those skilled in the art. Accordingly reference should be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. A process for puffing cereal grains which comprises maintaining steam pressure in an elongated confined zone having an orifice opening at its outlet end through which a high velocity current of steam continuously discharges, moving a stream of loose individual grains continuously through the steam atmosphere in said zone to said outlet end, and conveying the loose grains as they arrive at said outlet end through said orifice in said current of steam whereby a continuous stream of individual puffed grains is discharged from said zone.

2. The process defined in claim 1, the quality of the steam leaving said zone through said orifice ranging from substantially dry saturated steam to about 60 superheat.

3. The process defined in claim 1, the steam pressure at the outlet end of said zone ranging from about 100 lbs/sq. in. to about 160 lbs/sq. in.

4. The process defined in claim 1, said grain being preheated to a temperature in the range of 190-260 F. before entering said zone.

5. A process for putting cereal grains which comprises continuously moving a stream of loose individual grains through an elongated confined zone having a steam exhaust passage adjacent its inlet end and a discharge orifice adjacent its outlet end while admitting steam under pressure to said zone adjacent said orifice, thereby filling said zone with an atmosphere of steam under pressure moving countercurrently to said stream of grain and causing a high velocity current of steam to escape continuously through said orifice, and moving said stream of grain into the path of said current of steam whereby individual loose grains are conveyed through said orifice at substantially the same velocity as that of said current.

6. The process defined in claim 5, the steam pressure in the outlet end of said zone being in the range of 100-160 lbs/sq. in.

7. The process defined in claim 6', the quality of the steam admitted to said zone ranging from the substantially dry saturated condition to about 60 superheat.

8. The process defined in claim 7, including the step of preheating the grain to a temperature of about l-260 F. before admitting it to said zone.

9. The process defined in claim 8, wherein the walls of said zone are heated to prevent substantial condensation thereon.

10. A process for pufiing cereal grains which comprises continuously moving loose individual grains through an elongated confined zone having at its outlet end an open discharge orifice larger than the maximum dimensions of the individual grains, and maintaining an atmosphere of steam under pressure in said zone and a high velocity current of steam through said orifice by continuously admitting steam to said zone, the loose individual grains reaching the outlet end of said zone being moved into the path of said current and conveyed freely through said orifice thereby. I

11. The process defined in claim 10, the steam pressure at the outlet end of said zone being in the approximate range of -160 lbs/sq. in.

12. The process defined in claim 11, the quality of the steam entering said orifice ranging from substantially dry saturated steam to about 60 superheat and the grain being preheated before entering said zone, whereby condensation of moisture on the grain is substantially prevented.

13. A process for puffing cereal grains which comprises the steps of preheating whole grains containing about 6-10% moisture to a temperature in the range of l90-260 F., continuously moving a stream of loose individual preheated grains through an elongated confined zone having at its outlet end an open discharge orifice larger than the maximum dimensions of the individual grains, and continuously admitting steam to said zone adjacent said orifice at a pressure in the approximate range of 100-160 lbs/sq. in. and of a quality ranging from substantially dry saturated steam to about 60 superheat. thereby maintaining a high velocity current ofv steam through said orifice, the loose individual grains reaching the outlet end of said zone being moved into the path of said current and conveyed freely through said orifice thereby.

CLIFTON F. HAUGHEY. REGINALD T. ERICKSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,442,304 Spencer et a1. Jan. 16, 1923 1,639,909 Suzuki Aug. 23, 1927 1,922,313 Mason Aug. 15, 1933 2,414,185 Andrews Jan. 14, 1947 2,539,991 Chapman Jan. 30, 1950 

1. A PROCESS FOR PUFFING CEREAL GRAINS WHICH COMPRISES MAINTAINING STEAM PRESSURE IN AN ELONGATED CONFINED ZONE HAVING AN ORIFICE OPENING AT ITS OUTLET END THROUGH WHICH A HIGH VELOCITY CURRENT OF STEAM CONTINUOUSLY DISCHARGES, MOVING A STREAM OF LOOSE INDIVIDUAL GRAINS CONTINUOUSLY THROUGH THE STEAM ATMOSPHERE IN SAID 